Precalibrated thermostatic latch assembly



March 2, 1965 K. w. KLEIN ETAL 3,171,930

PRECALIBRATED THERMOSTATIC LATCH ASSEMBLY Filed Jan. 2, 1963 K 2 Sheets-Sheet 1 nvvs/vrom: KE/TH W. KLE/N,

JAV/D 5. P0 WELL: BY M ATTORNEY.

March 2, 1965 K. w. KLEIN ETAL 3,171,930

PRECALIBRATED THERMOSTATIC LATCH ASSEMBLY Filed Jan. 2, 1963 2 Sheets-Sheet 2- TR/PPED nvvmvrons: KE/TH W KLE/N,

DAV/0 5. P WELL, y M M ATTORNEY.

United States Patent 3,171,930 PRECALIBRATED THERMOSTATIC LATCH ASSEMBLY Keith W. Klein, Sunsbury, and David B. Powell, Bristol,

C0nn., assignors to General Electric Company, a corporation of New York Filed Jan. 2, 1963, Ser. No. 248,923 Claims. (Cl. 200-116) Our invention relates to thermostatic latch mechanisms, and particularly to improvements in a precalibrated thermostatic latch of the type shown in Patent 2,786,917 issued to Robert T. Casey on March 26, 1957 and assigned to the same assignee as the present invention. As illustrated in the foregoing patent such a precalibrated thermostatic latch is especially well adapted as an overlap trip device in small air circuit breakers of the manually operable current responsively tripped type. In such applications the latch is usually in the form of a deformable bimetallic strip and is heated either directly or indirectly by current through the circuit breaker con tacts.

The foregoing patent discloses a U-shaped bimetallic strip or hairpin loosely mounted at its bight in a circuit breaker casing and having a pair of legs adapted to spread apart when heated. One leg carries a latch detent engageable with a movable trip member and the other leg engages an abutment on the trip member to position the bimetal, the bimetal being biased to latching position by a spring engaging the latching leg.

It is a principal object of our invention to provide an improved thermostatic latch of the precalibrated type in which resistance to unlatching movement is reduced to a minimum.

A further object of our invention is to provide a precalibrated thermostatic latch in which thermal calibration is unaffected by any biasing force on the latch detent.

Still another object of our invention is to provide an adjustable precalibrated thermostatic latch in which latch friction is wholly eliminated over a major or appreciable part of the unlatching movement.

It is a particular object of our invention to provide a thermostatic latch assembly for circuit breaker trip devices which has an inherent precalibration dependent only upon certain initial dimensions of the cooperating trip member and latch member, and independent of any other parts of the circuit breaker assembly.

In carrying out our invention in one preferred embodiment especially adapted for small circuit breakers of the type described, we provide a releasable tripping member biased to trip position and formed to provide a latching shoulder and an abutment in predetermined fixed spacial relation. A thermally deformable latch member loosely mounted in the casing extends between the abutment and latch shoulder of the tripping member and carries a latch detent engageable with the shoulder. When heated, a positioning portion of the latch member engages the abutment and dimensional change of the latch member due to thermal deformation releases the latch detent. Since the latch member coacts with the trip member in both action and reaction thermal calibration is determined solely by the initialdimensions of these two parts only. In a simplified and preferred form of the invention the latch member is formed of asingle U-shaped strip of bimetal having substantially parallel legs oppositely deformable when heated. One leg of the bimetal hairpin carries a latch detent and the other leg acts by engagement with the abutment of the trip member to position the bimetal for latch releasing action. The bimetal hairpin is loosely pivotally mounted 3,171,930 Patented Mar. 2, 1965 at its bight and biased to latching position. In normal cold latched position the positioning leg of the bimetal may be spaced from or in light contact with the abutment on the tripping member. The bimetal is biased to latching position by means of a resilient member in engagement with its positioning leg only.

Further objects and advantages of our invention will be apparent to those skilled in the art from the following' detailed specification taken in conjunction with the accompanying drawings in which:

FIG. 1 is an elevational view of an electric circuit breaker including a trip unit embodying our invention and showing the circuit breaker mechanism in the off or circuit opening position with the trip unit in latched position;

FIG. 2 is an elevational view of the circuit breaker shown at FIG. 1 with the trip unit in latched position and the operating mechanism in manual on or circuitclosing position;

FIG. 3 is a fragmentary elevational view of the circuit breaker shown at FIGS. 1 and 2 showing the trip unit in released position and the circuit breaker mechanism in trip free position, i.e. open-circuit position with the manual handle held in the on position; and

FIGS. 4 and 5 are detail elevational views of circuit breaker trip units similar to those of FIGS. 1-3 inclusive but illustrating our invention in certain other embodiments.

Referring now to the drawing and particularly to FIGS. 1 and 2, we have illustrated our invention as applied to a small manually operable current-responsively tripped electric circuit breaker of the molded case type having an operatingmechanism of a kind described and claimed in a co-pending patent application S.N. 242,424, filed December 5, 1962 by David B. Powell and assigned to the same assignee as the instant application. The circuit breaker illustrated is contained in a unitary casing 10 preferably formed of a suitable molded unsulating material and illustrated with one side of the casingremoved to display the operating mechanism. The circuit breaker comprises a plug-in line terminal clip 11 mounted in the casing 10 and shown in position upon a flat o1 blade-like bus bar 11a. A load terminal member 12 is mounted adjacent an opening in one end wall of the casing and arranged for cooperation with a quick detachable spring connector 13 to receive a load conductor 12a- The load terminal 12 carries at its inner end a stationary; contact 14; a cooperating movable contactJS is mounted upon avpivoted contact arm 16. The contact arm 16 is pivotally mounted in the casing upon a fixed pivot pin 17 and biased to open circuit position by a compression spring 18 disposed between the contact arm 16 and a spring seat in the casing 10.

The operating mechanism for manually and automatically moving the contact arm 16 between open circuit and closed circuit positions comprises a releasable tripping member 19 shown asaflat plate of insulating material, loosely pivotally mounted upon a pivot, pin 20 and haivng at its side adjacent the contact arm 16 a cam surface 21. The cam surface 21 is formed in two parts providing between them an apex point with which a cam follower cooperates with an overcenter locking action to be more fullydescribedhereinafter. The releasable tripping member 19 is normally restrained against tripping movement by means of a thermostatic latch embodying our invention and thus provides a normally fixed cam surface 21 for cooperation with the movable contact arm' 16 in manual closing and opening operation.

The lateral edge of the contact arm 16 adjacent the normally fixed cam surface 21 constitutes a cooperating cam surface 22 of essentially linear configuration and is disposed to converge toward the cam surface 21 in the open circuit position of the parts illustrated at FIG. 1. For manual closing and opening operation there is provided a movable wedging roller 23 rotatably mounted upon a pivot pin 24 at the free end of a swinging link 25. The link25 is pivotally mounted eccentrically upon a rotary handle member 26 carried by the pivot pin 20. The handle member 26 is provided with a radial arm 27 which'extends through the upper end wall of the casing 10 to serve as a handle lever. The link 25 is swingably mounted upon an internalarm of the handle 26 by means of a pin 28. The upper portion of the handle member 26 is provided with an arcuate rim 31, one end of which serves as an abutment or shoulder to engage the releasable tripping member 19 when released and return it to latched position. as a handle abutment for one arm of a torsion spring 29 which encircles the fixed pivot pin and has a second arm engaging a fixed stop 30. The spring 29 biases the rotary handle 26 to the off position shown at FIG; 1.

It will now be evident that in manual operation when the handle lever 27 is moved from the position of FIG. 1 to the position of FIG. 2, the swingable actuating link is moved downwardly and the wedging roller 23 forced between the cam surfaces 21; and 22, respectively, of the releasable tripping member 19 and the movable contact arm 16 The roller 23 moves overcenter on the apex point of the fixed cam surface 21 and locks the movable contact arm 16in its closed circuit position against the bias of the spring 18 as shown at FIG. 2. In this position the force of the spring 18upon the contact arm 16 is transmitted through the wedging roller or cam follower 23 to the releasable tripping member 19 by pressure against the normally fixed cam surface 21. This pressure from the contact bias spring serves, in the circuit-closing position of the mechanism, to bias the releasable tripping member 19 for"counterclockwise movement'(as shown in the draw .ings) to a released or tripping position.

The tripping member 19 is normally restrained against such movement by means of an improved thermostatic latch or trip device described hereinafter. I

'To restrain the movable tripping member against movement to'released position under the bias of the movable contact spring 18, 'we provide a thermally deformable latching member shown as a generally U-shaped strip 40 of bimetallic material loosely pivotally mounted at its bight'upon'a casing abutment 41 and providing at the free end'of one'leg a bent-overportion constituting a latching detent 42. 'As shown at FIGS. 1 and 2, the latching detent is in engagement with a latching shoulder 43 formed upon the releasable tripping member 19, the bimetallic latchingmember '40 being biased to this latch-engaging position by means of a compression spring 44 interposed between the other leg 40a of the bimetal and a spring seat in the casing 10. The legs of the bimetal member 40 are arranged to'deflect in opposite directions upon heating, and in the illustrated embodiment of the invention they are arranged to separate or open up the bimetal hairpin upon the application of heat. The leg 40a opposite that carrying the detent 42 is disposed in cold or unheated condition adjacent an abutment 45 on the trippingmember 19 If not initially in engagement with the abutment 45, "the leg 40a moves to engaging position when heated and serves-in either case to position the bimetal 4'0{with-'respec't to the tripping member 19 in overload operation. The leg 40a is referred to herein as a positioning leg of the latching member.

In the illustrated embodiment of the invention the bimetal latching member 40 is shown as directly heated by conductive "inclusion in the electric circuit through the contacts l4rand'l5. This circuit includes a flexible conductor 46 connectedbetween the movable contact member 16 and the positioning'leg 40a of the bimetal 40 and a flexible conductor 47 connected between the latch leg of thebimeta'l 40 and the line terminal clip 11. It will of The opposite end of the arcuate rim 31 actscourse be understood that if desired the member 40 may be indirectly heated.

In order to provide rapid tripping operation upon very high overload or short circuit current the latch leg 40 of the bimetal 40 carries a U-shaped magnetizable member 48 through which the flexible conductor 47 passes to form an electromagnet. A cooperating armature member 49 of magnetizable material is fixedly mounted in the casing 10 to attractthe electromagnet and directly trip the latch 42, 43 under short circuit conditions.

In FIGS. 1 and 2 the U- shaped bimetallic latching member 40 is illustratedin its normal initial or unheated condition. In this condition the free ends of the positioning leg 40a and the latch leg are separated by a predetermined initial distance determined by design andmanufacturing tolerance. Also, the positioning abutment 45 and the outer edge of the latching shoulder 43 on the releasabletripping member 19 are spaced apart by a predetermined fixed amount greater than the initial separation between the legs of the latching member 40, It is evident that with a U-shaped latch member of any pre determined design and initial configuration a predetermined temperature rise, and thus predetermined overload current, is required to separate the free ends of the legs by an amountslightly greater than the distance between the abutment 45 and latch shoulder 43. This predeter mined amount of heating from cold or initial position may be varied by changing the initial position of the positioning leg 40a with respect to the abutment 45. For a bimetallic latch member of any predetermined material and cross section a minimum calibration may be attained if the positioning leg 40a is initially in engagement with the abutment 45. For higher calibration the positioning leg 40a may be designed to assume an initial position spaced away from the abutment 45, as shown at FIGS. 1 and 2. l l i It will be evident that when overload current sufficient to cause appreciable heatingof the bimetal 40 occurs, the positioning leg 40):: first moves counterclockwise (as shown in the drawings) into engagement with the abutment 45 and that thereafter further separation of the bimetal legs cause clockwise movement of the latch leg to: release the latch, the positioning leg 40a positioning the bimetal hairpin again the abutment 45. 'When the latch 42, 43 is released, the tripping member 19 moves upwardly under the influence of the contact spring 18 and allows the contacts to separate in the mannershown at FIG. 3. In this figure the legs of the birnetalhairpin are shown sufficiently diverged by thermal deformation to release the trip latch. The position of the parts shown at FIG. 3 is not a stable position because the handle spring 29 will normally effect automatic reset of the parts to the position of FIG. 1 as soon as the handle 27 is released. In FIG. 3 the parts are shown in what is usually referred to as trip-free position to illustrate tripping movement of the trippingmember 19 if the handle is held abutment 45 and the latch leg need not work against the bias. Moreover, when the positioning leg is initially set at a position spaced from the abutment 45 high thermal settings may be attained without any increase in latchoverlap. This is because the tripping member 19 includes a portion 43A extending substantially at right angles to the shoulder portion 43, which the end of the latch detent 42 abuts against, to thereby limit the amount of overlap of the latchdetent 42 on the shoulder 43., Thus latch overlap may be set at a fixed minimum and opposes thermal unlatching action only over a small terminal portion of the unlatching deformation.

At FIG. '4 we have shown another embodiment of our invention in which the U-shaped latching member is formed with only aportion of the latch leg made of bimetal. It will now be evident to those skilled in the art that if desired such a U-shaped latching member may also be constructed with only the positioning leg 40a or a part thereof made of bimetal. FIG. 4 also serves to illustrate that if desired the initial or unheated configuration of the latching member may be such that the positioning leg is in light contacting engagement with the positioning abutment on the tripping member.

In FIG. 5 we have illustrated still another embodiment of our invention in which the abutment of the tripping member 19 is formed as an eccentric cam a so that the spacing between the latch shoulder 43 and the positioning abutment may be varied slightly to correct for manufac turing inaccuracies in either the tripping member or the latching member, or to vary the overload calibration within predetermined limits.

While we have described a preferred embodiment of our invention by way of illustration, many modifications will occur to those skilled in the art. For example, it will be evident that the initial angular relation between the latch leg and positioning leg of bimetallic latching member is not necessarily one of substantial parallelism. Indeed, even the two-legged configuration itself is not essential, but it is convenient. With such a structure any elongated deformable member of two-legged configuration may be utilized so long as the initial angular relation (including alignment) of the legs is changed by thermal deformation. Similarly it will be evident that a U-shaped bimetal or hairpin need not necessarily open up or diverge upon heating but may, if desired, close in response to heat, it being only necessary that the legs de fleet in opposite directions upon the application of heat. It will be evident, therefore, that we intend in the appended claims to cover all such modifications as fall within the true spirit and scope of our invention.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. A precalibrated thermal latch assembly comprising:

(a) a support,

' (b) a tripping member pivotally mounted on said support, 7

(c) said tripping member having a latch shoulder portion,

(d) said tripping member having an abutment portion spaced from said latch shoulder portion in fixed predetermined spaced relation,

(e) biasing means carried by said support biasing said tripping member for rotation in a predetermined direction,

(f) a thermally deform-able latching member supported on said support, said thermally deformable member having a latch detent portion in engagement with said latch shoulder and preventing rotation of said tripping member in said predetermined direction,

g) said thermally deformable latching member having a positioning portion adjacent said abutment portion of said tripping member,

(h) said positioning portion of said thermally deformable member being spaced from said detent portion a predetermined distance at a corresponding predetermined temperature of said member, and

(i) biasing means acting on said positioning portion of said thermally deformable member and biasing said member in a direction to move said detent portion into latching engagement with said latch shoulder portion of said tripping member,

(i) said thermally deformable member having a high expansion side and a low expansion side, said side being arranged .so that upon an increase in temperature said member deforms and moves said positioning portion away from said detent portion in the same direction as said biasing means tends to move said positioning portion, whereby following engagement of said positioning portion with said abutment, said thermally deformable member warps to move said detent portion away from said latch shoulder portion without opposition by said biasing means.

' 2. A precalibrated thermal latch assembly comprising: (a) a support,

(1)) a tripping member pivotally supported on said support,

(0) said tripping member having a latch shoulder portion,

(d) said tripping member having an abutment portion spaced from said shoulder portion in fixed predetermined spaced relation,

(e) biasing means carried by said support biasing said tripping member for rotation in a predetermined direction,

(f) a thermally deformable latching member supported on said support and having a pair of legs connected together at one end to form a generally U-shaped configuration,

(g) a first one of said legs of said latching member having a latch detent portion adjacent the outer end thereof in engagement with said latch shoulder of said tripping member in said predetermined direction,

(h) the other leg of said thermally deformable latching member comprising a positioning portion adjacent said abutment portion of said tripping member,

(i) said positioning portion of said second leg being spaced from said detent portion of said first leg a predetermined distance at a corresponding predetermined temperature of said latching member,

(j) biasing means acting directly on said second leg of said thermally deformable latching member and biasing said member in a direction to move said detent portion of said first leg into latching engagement with said latch shoulder portion of said tripping member,

(k) each of said legs of said thermally deformable member having a high expansion side and a low expansion side, said high expansion sides of said legs facing each other at the inside of said U so that upon an increase in temperature said member deforms so as to move said legs away from each other, whereby following engagement of said positioning portion of said second leg with said abutment, said thermally deformable member moves said detent portion away from said latch portion without opposition by said biasing means.

3. A precalibrated thermal latch assembly as set forth in claim 2 wherein said assembly includes an abutment fixedly carried by said support between said legs of said thermally deform-able latching member, and said biasing means for said latching member comprises a compression spring acting between said support abutment and said second leg of said thermally deformable latching member.

4. A precalibrated thermal latch assembly comprising:

(a) a support,

(b) a tripping member pivotally mounted on said support,

(c) said tripping member having a latch shoulder portion,

(d) said tripping member having an abutment portion spaced from said latch shoulder portion in fixed predetermined spaced relation,

(e) biasing means carried by said support biasing said tripping member for rotation in a predetermined direction,

(f) a thermally deformable latching member supported on said support, said thermally deformable latching member having a latch detent portion in engagement with said latch shoulder and preventing rotation of said tripping member in said predetermined direction,

(g) said thermally deformable latching member having a positioning portion adjacent said abutment portion of said tripping member, 7

(h) said positioning portion of said thermally deformable latching member being spaced from said detent portion a predetermined distance at a corresponding predetermined temperature of said latching member,

(i) said tripping member including astop portion adjacent said shoulder portion and extending substantially at right angles thereto,

(j) biasing means acting on said thermally deformable latching member and biasing said member in a direction to move said detent portion into latching engagement with said latch shoulder portion of said tripping member,

(k) said positioning portion of said thermally deformable latching member being out of contact with said abutment portion of said tripping member at a predetermined temperature, movement of said thermally deformablerlatching member by said biasing means at said predetermined temperature being limited by engagement of said detent portion with said stop portion of said tripping member, whereby a predeterrnined relatively small amount of latch overlap is provided and a relatively large amount of deflection of said thermally deformable latching member is permitted,

(1) said thermally deformable member having a high expansion side and a low expansion side, said sides being arranged so that upon an increase in temperature said member deforms and moves said positioning portion toward said abutment portion and said detent portion away from said shoulder portion.

' 5. A precalibrated thermal latch assembly comprising:

(a) a support,

, (b) a tripping member pivotally mounted on said support,

(c) said tripping member having a latch shoulder portion, 7

(d) said tripping member having an abutment portion spaced from said latchshoulder portion in fixed predetermined spaced relation,

(e) biasing means carried by said support biasing said tripping member for rotation in a predetermined direction,

(f) a thermally deformable latching member supported ontsaid support and havingapair of legs connected together at one end to form a generally U-shaped configuration, said thermally deformable latching member having alatch detent portion'on one leg thereof in engagementwith said latch Shoulder andpreventing rotation of said tripping member in said predetermined direction,

(g) the other leg of said thermally deformable-latching 'member including a positioning portion adjacent said abutment portion of said tripping member,

(11) said positioning portion of said thermally deformable latching member being spaced from said detent portion a predetermined distance at a corresponding predetermined temperature of said latching member,

(i) said tripping member including a stop portion adjacent said shoulderportion and extending substantially at right angles thereto,

(j) biasing means acting on said thermally deformable,

latching member and bias said member in a direction to move said detent portion into latching engagement with said latch shoulder portion of said tripping member,

(k) said positioning portion of said thermally deformable latching member being out of contact with said abutment portion of said tripping member at a predetermined temperature, movement of said thermally deformable latching member by said biasing means at said predetermined temperature being limited by engagement of said detent portion with said stop portion of said tripping member, whereby a predetermined relatively small amount of latch overlap-is provided and a relatively large amount of deflection of said thermally deformable latching member is' References Cited by the Examiner UNITED STATES PATENTS 2,692,929 10/54 Ericson 200-116 2,786,917 3/57 Casey 200-416 BERNARD 'A. GILHEANY, Primary Examiner. 

1. A PRECALIBRATED THERMAL LATCH ASSEMBLY COMPRISING: (A) A SUPPORT, (B) A TRIPPING MEMBER PIVOTALLY MOUTNED ON SAID SUPPORT, (C) SAID TRIPPING MEMBER HAVING A LATCH SHOULDER PORTION, (D) SAID TRIPPING MEMBER HAVING AN ABUTMENT PORTION SPACED FROM SAID LATCH SHOULDER PORTION IN FIXED PREDETERMINED SPACED RELATION, (E) BIASING MEANS CARRIED BY SAID SUPPORT BIASING SAID TRIPPING MEMBER FOR ROTATION IN A PREDETERMINED DIRECTION, (F) A THERMALLY DEFORMABLE LATCHING MEMBER SUPPORTED ON SAID SUPPORT, SAID THERMALLY DEFORMABLE MEMBER HAVING A LATCH DETENT PORTION IN ENGAGEMENT WITH SAID LATCH SHOULDER AND PREVENTING ROTATION OF SAID TRIPPING MEMBER IN SAID PREDETERMINED DIRECTION, (G) SAID THERMALLY DEFORMABLE LATCHING MEMBER HAVING A POSITIONING PORTION ADJACENT SAID ABUTMENT PORTION OF SAID TRIPPING MEMBER, (H) SAID POSITIONING PORTION OF SAID THERMALLY DEFORMABLE MEMBER BEING SPACED FROM SAID DETENT PORTION A PREDETERMINED DISTANCE AT A CORRESPONDING PREDETERMINED TEMPERATURE OF SAID MEMBER, AND (I) BIASING MEANS ACTING ON SAID POSITIONING PORTION OF SAID THERMALLY DEFORMABLE MEMBER AND BIASING SAID MEMBER IN A DIRECTION TO MOVE SAID DETENT PORTION INTO LATCHING ENGAGEMENT WITH SAID LATCH SHOULDER PORTION OF SAID TRIPPING MEMBER, (J) SAID THERMALLY DEFORMABLE MEMBER HAVING A HIGH EXPANSION SIDE AND A LOW EXPANSION SIDE, SAID SIDE BEING ARRANGED SO THAT UPON AN INCREASE IN TEMPERATURE SAID MEMBER DEFORMS AND MOVES SAID POSITIONING PORTION AWAY FROM SAID DETENT PORTION IN THE SAME DIRECTION AS SAID BIASING MEANS TENDS TO MOVE SAID POSITIONING PORTION, WHEREBY FOLLOWING ENGAGEMENT OF SAID POSITIONING PORTION WITH SAID ABUTMENT, SAID THERMALLY DEFORMABLE MEMBER WARPS TO MOVE SAID DETENT PORTION AWAY FROM SAID LATCH SHOULDER PORTION WITHOUT OPPOSITION BY SAID BIASING MEANS. 